Scientists fear mass extinction as oceans choke - ABC News
Low oxygen levels, which have been found along south-eastern Australia, are known to increase stress on fish. (Reuters: Ho New)
Australian scientists fear the planet is on the brink of another mass extinction as ocean dead zones continue to grow in size and number.
More than 400 ocean dead zones - areas so low in oxygen that sea life cannot survive - have been reported by oceanographers around the world between 2000 and 2008.
That is compared with 300 in the 1990s and 120 in the 1980s.
Professor Ove Hoegh-Guldberg, of the ARC Centre of Excellence for Coral Reef Studies (CoECRS) and from the University of Queensland, says there is growing evidence that declining oxygen levels in the ocean have played a major role in at least four of the planet's five mass extinctions.
'Until recently the best hypothesis for them was a meteor strike,' he said.
'So 65 million years ago they've got very good evidence ... all the dinosaurs died because of smoke and stuff in the atmosphere from a meteor strike.
'But with the four other mass extinction events, one of the best explanations now is that these periods were preceded by an increase of volcanic activity, and that volcanic activity caused a change in ocean circulation.
'Just as we are seeing at a smaller scale today, huge parts of the ocean became anoxic at depth.
'The consequence of that is that you had increased amounts of rotten egg gas, hydrogen sulfide, going up into the atmosphere, and that is thought to be what may have caused some of these other extinction events.'
Professor Hoegh-Guldberg says up to 90 per cent of life has perished in previous mass extinctions and that a similar loss of life could occur in the next 100 years.
'We're already having another mass extinction due to humans wiping out life and so on, but it looks like it could get as high as those previous events,' he said.
'So it's the combination of this alteration to coastlines, climate change and everything, that has a lot of us worried we are going to drive the sixth extinction event and it will happen over the next 100 years because we are interfering with the things that keep species alive.
'Ocean ecosystems are in a lot of trouble and it all bears the hallmarks of human interference.
'We are changing the way the Earth's oceans work, shifting them to entirely new states, which we have not seen before.'
He says while it is impossible to predict the future, in a century from now the world will be vastly different.
'A world without the Great Barrier Reef, where you don't have the pleasure of going to see wild places any more,' he said.
'We might be able to struggle on with much lower population densities, but ultimately it won't be the world we have today.
'The idea of walking in the Daintree will be a forgotten concept because these changes have occurred.'
Hearts and lungs
Scientists say ocean dead zones, which vary in size from one square kilometre to 70,000 square kilometres, have been found all over the world.
Particular hotspots include the Gulf of Mexico, off Namibia in the South Atlantic, in the Bay of Bengal, in the Baltic, the Black Sea, the tropical South Pacific, off China and south-eastern Australia.
'We're seeing an expansion of areas of the ocean which are very low in oxygen and also very low in nutrients,' Professor Hoegh-Guldberg said.
'Climate change is driving changes to water circulation - so winds, strange weather patterns, have a consequence for how the ocean turns over and aerates and so on, and it's the winds which are delivering a lot of organic compounds into the deep sea.
'At the same time we are putting a lot of fertiliser off coastlines, those sorts of things are incubating these deep water anoxic zones.
'So it's the combination of those two things that are having a big change on how the ocean works.'
He says organic matter building up in the sea is a huge problem.
'You get enormous amounts of organic carbon building up at depth, bacteria then likes to break down that organic matter and bacteria uses up the oxygen,' he said.
'So then what you get is a substantial drop in oxygen - that then has the consequences for fishers, for the productivity of coastlines and so on.'
Destructive path
Associate Professor Mark McCormick, also of CoECRS and from James Cook University, says low oxygen levels increase stress on fish.
'We know from our recent work that increases in stress result in deformities, leading to poorer survival of fish larvae,' he said.
'It has also been found they can cause fish to have smaller ovaries, produce fewer eggs, so larvae are also smaller and less likely to survive.'
Professor Hoegh-Guldberg says the problem is not as significant in Australia as other parts of the world, but that it is heading along the same, destructive path.
'We've been altering coastal areas, delivering nutrients into the ocean, and of course you see the Great Barrier Reef, which has been quite damaged due to nutrient run-off,' he said.
'But the point is that our activities on land have a big influence on what goes on in the oceans and now we are starting to reap the harvest of those changes.'
He says the heart and lungs of the planet are being tampered with.
'We are starting to see changes in the ocean's ability to produce oxygen and to produce food and produce all of the ecosystem's services that are so important to not only us, but all of the other organisms on the planet,' he said.
'It's mucking around with the heart and lungs of the planet - that's essentially what the oceans are, a huge respiratory system.
'We damage them, the consequences could be very serious.'
Professor Hoegh-Guldberg says while the dead zones may only exist in pockets of ocean today, it will affect a far greater area in the future unless steps are taken to reduce the impact of human activities on the world's oceans and their life.
- Sent using Google Toolbar"
Tuesday, November 30, 2010
Tuesday, November 23, 2010
Shark protection industry at work?
Lurking beyond our fatal shores | The Australian: "Lurking beyond our fatal shores
SHARKS are a summer certainty, but how afraid should we be?
IT'S summer in Australia and, as always, the crowds flock to our golden beaches to paddle, swim and surf. It's our heritage and nothing can keep us away. Not even sharks.
Not even the brutal savagery of a shark attack that can dismember and kill. After all, statistics tell us only one person a year dies from a shark attack in Australia. That's on average.
Not bad odds, we tell ourselves. Tens of thousands of us frolic in our coastal waters every day without fear of sharks. Indeed, most Australians have never seen a shark. The risk of attack is not worth worrying about. It's more likely we'll get run over by a truck.
Yet that risk is a reality, even though the bell tolls slowly.
On August 17 this year, father of two Nicholas Edwards was the most recent to die from a shark attack in Australian waters. He was attacked by a great white shark while surfing at Gracetown, near Margaret River 280km south of Perth, the same location where Bradley Adrian Smith was mauled to death six years earlier.
Dive tour guide Elyse Frankcom, 19, was luckier late last month when she survived a great white attack near Rockingham, 50km south of Perth, not far from where Brian Guest was fatally mauled in December 2008.
Sharks do bite. The prevailing opinion, however, is that most attacks are the result of mistaken identity. In the water, from below, humans can resemble seals or turtles. Or it may be a case of simple curiosity. The shark will bite and quickly let go when it realises this is not its natural food.
During months of research for my book Shark! Killer Tales from the Dangerous Depths, I interviewed a wide range of experts from former shark hunters to marine scientists and researchers.
The overwhelming opinion is that fear of sharks is unwarranted and the danger factor almost zero. That fear, they say, is a result of fictitious accounts of monster sharks such as that portrayed in Peter Benchley's book Jaws and the Steven Spielberg movie of the same name that became a worldwide hit in 1975.
Mass killing of sharks followed, leading to several species becoming endangered. Environmentalists claim the killing mood and fear of sharks is exacerbated by sensationalist reports in the media, a trend they say continues whenever an attack occurs.
But there are those who disagree vehemently and warn that the soft attitude to sharks gives people a false and dangerous sense of security.
Fritz Herscheid is one of them. Herscheid, a former salvage diver who operated a lucrative business recovering scrap metal and shipwreck treasures in Papua New Guinea waters during the 1960s and 70s, had to share his encounters with sharks, including tigers and hammerheads, and he didn't like it.
'I would like to see every dangerous shark dead,' Herscheid insists. 'If I could find a genetic way of killing all whites, tigers and bull sharks, I'd kill all of them.'
Bold words, but Herscheid, who owns a broker business in Cairns, refuses to back off.
'Humans come first and animals come second. We have as much right in the water as them and if they can't be kept away from people, then get rid of them.
'My son is a keen surfer, and if he was killed by a shark I'd be a Vic Hislop, all my life killing sharks.'
Hislop's name is known to most Australians. Think sharks, think Hislop, shark hunter.
Hislop hasn't changed his attitude towards sharks in four decades. He maintains hardcore greenies cover up the truth about shark attacks and that many people presumed missing and drowned at sea have in fact been taken by sharks.
He is mocked in scientific circles as a shark killer with no real knowledge of the creatures he hunts. To others, however, he is a valiant sea warrior ridding our coastline of man-eating predators.
Prominent underwater photographers and documentary filmmakers Ron and Valerie Taylor summed up the prevailing conservation attitude to Hislop when Ron Taylor told me in 1991 that they refused to discuss the man or his claims.
'Hislop is the only person in the world we don't want to be associated with,' he said.
'No wonder!' Hislop replied. 'They won't front me on television to debate this issue. I've challenged them, but they're not game because they know I can back up what I'm saying.'
After a spate of shark attacks around the Australian coast early last year, Hislop was adamant in his long-held belief that bureaucrats and government officials, aided and abetted by conservation groups and tourism dive operators, lead a conspiracy to cover up the true figures relating to shark attack fatalities.
'The shark protection industry doesn't like me because I tell the truth,' Hislop says.
'I won't change. I've been right all along. Shark fatalities around Australia and the world are continually manipulated to suit the shark industry.'
Hislop continues to hunt sharks from his base at Hervey Bay, Queensland, where his popular shark show continues to attract enthusiastic crowds.
'The people who are hiding the truth about great white sharks are the ones who will stay out of the water and die in bed. They have no worries, but what about their children and grandchildren?
'Some of them are sure to be taken because I predict the coming years will see a great increase in fatal attacks, all because of blatant lies and bureaucratic stupidity.'
One of the issues that intrigues me is the question of so-called rogue sharks - sometimes referred to as serial killers of the sea - those that attack and kill humans in numbers, at the same time, in the same place.
Do rogue sharks exist or are multiple attacks merely coincidental and random? That such attacks sometimes occur is a fact, but the reasons why are in dispute.
In one little-known but terrifying incident, a tiger shark attacked three people in one day in Madang Harbour in PNG, killing two.
Nine days later it struck again, claiming its third human life.
The killing spree began on February 7, 1996. On that day, the calm waters of this peaceful town were turned into a bloody slaughterhouse as the shark stalked the harbour. In little more than a week, three lives were lost in four attacks.
Tim Rowland, an expatriate Australian who has operated adventure dive tours in PNG and Solomon Islands for the past four decades, said it wasn't until the next day that the attacks became general knowledge.
'Very few people would have known on the day they happened,' Rowland told me. 'The two who went in after the first wouldn't have known.
'That shark basically had breakfast, lunch and dinner.'
A week later, Rowland was scuba diving with a student when they were confronted by a 4m tiger shark. Rowland had entered the water knowing the risk, but experience and common sense ensured he was alert to danger.
'We were supposed to do a surface swim but because I thought the shark might still be around I decided we'd go underwater,' Rowland says.
'I'm glad we did because that's when we ran into him. We were in a little alcove when the shark came in over the top and brushed against me.
'I heard the student scream through his regulator, so I grabbed him and pulled him down to the bottom. I was certain this was the shark that had killed those people.'
Rowland punched the shark as it made several passes before moving off.
'I was amazed at how slow the shark was moving. It was like slow motion, and I was thinking when is he going to open his mouth and take a chomp at us. He was a big shark.'
Rowland and the student made it to safety. A 4m tiger shark was caught 11 days after the first attacks. He has no doubt it was Madang's killer shark.
Australian surgeon V. M. Coppleson was one of the first modern scientists to develop the rogue shark theory in his attempt to understand and explain why sharks occasionally attack humans in numbers.
In his 1958 book Shark Attack, Coppleson used the term rogue many times as he documented multiple attacks across the world, including several serial fatal attack patterns on Sydney's beaches in the 20s and 30s.
He also recorded a series of five fatal shark attacks in four years on the sparsely populated beaches north of Cairns in the 40s.
In an article published in the Medical Journal of Australia, Coppleson wrote: 'A rogue shark, if the theory is correct, and evidence appears to prove it to the hilt - like the man-eating tiger - is a killer which, having experienced the deadly sport of killing or mauling a human, goes in search of similar game. The theory is supported by the pattern and frequency of many attacks.'
The most famous example of multiple shark attacks took place on the New Jersey coast of the US during the summer of 1916, when four people were killed in 12 days. Such a series of attacks was unknown at the time.
Disbelief, fear and confusion reigned until a great white shark was caught in Raritan Bay with human bones and flesh in its stomach.
In December 1957, the South African city of Durban was the focal point for what is believed to be a world record for the most shark attacks in a single place in a short time.
Beginning in what became known as Black December and continuing for 107 days, seven attacks took place at unprotected beaches south of the city, claiming five lives.
But the rogue shark concept is almost universally dismissed in contemporary scientific thought.
John West, who collates statistics for Sydney's Taronga Zoo's Australian Shark Attack File, rejects the notion of rogue sharks that specifically target humans.
He points out that Coppleson's rogue shark theory, while credible at the time, is discredited.
'Modern analysis of shark attack data does not support the theory of a rogue shark as a viable explanation for the vast majority of shark attacks, whether clustered or not,' West says.
'Some of the clusters of attacks he noted were many kilometres apart, or months or even years apart, and could not realistically relate to a single rogue shark.'
John Stevens, a senior principal research scientist at CSIRO Marine and Atmospheric Research in Hobart who has 30 years' experience studying sharks, agrees that Coppleson's rogue shark theory is just that, a theory.
'There is no scientific basis for it. It's more likely that favourable conditions for sharks at the time of an attack just brought several into the area around the same time,' Stevens says.
'There is no evidence for one individual being responsible for a chain of attacks.'
Shark attack survivor Rodney Fox, the diver who was almost bitten in half by a great white in 1963 and now owns and operates the Rodney Fox Great White Shark Expeditions at Port Lincoln in South Australia, agrees.
'There is no evidence that a rogue shark, a killer with a taste for human blood, has ever existed in the past or exists now,' he says.
But it's hard to deny the evidence of some multiple attacks being the deadly work of a single shark, and that day of horror in Madang Harbour comes to mind.
Three attacks in one day. Two people dead. One shark.
Robert Reid is the author of Shark! Killer Tales from the Dangerous Depths published by Allen & Unwin and available next Tuesday.
- Sent using Google Toolbar"
SHARKS are a summer certainty, but how afraid should we be?
IT'S summer in Australia and, as always, the crowds flock to our golden beaches to paddle, swim and surf. It's our heritage and nothing can keep us away. Not even sharks.
Not even the brutal savagery of a shark attack that can dismember and kill. After all, statistics tell us only one person a year dies from a shark attack in Australia. That's on average.
Not bad odds, we tell ourselves. Tens of thousands of us frolic in our coastal waters every day without fear of sharks. Indeed, most Australians have never seen a shark. The risk of attack is not worth worrying about. It's more likely we'll get run over by a truck.
Yet that risk is a reality, even though the bell tolls slowly.
On August 17 this year, father of two Nicholas Edwards was the most recent to die from a shark attack in Australian waters. He was attacked by a great white shark while surfing at Gracetown, near Margaret River 280km south of Perth, the same location where Bradley Adrian Smith was mauled to death six years earlier.
Dive tour guide Elyse Frankcom, 19, was luckier late last month when she survived a great white attack near Rockingham, 50km south of Perth, not far from where Brian Guest was fatally mauled in December 2008.
Sharks do bite. The prevailing opinion, however, is that most attacks are the result of mistaken identity. In the water, from below, humans can resemble seals or turtles. Or it may be a case of simple curiosity. The shark will bite and quickly let go when it realises this is not its natural food.
During months of research for my book Shark! Killer Tales from the Dangerous Depths, I interviewed a wide range of experts from former shark hunters to marine scientists and researchers.
The overwhelming opinion is that fear of sharks is unwarranted and the danger factor almost zero. That fear, they say, is a result of fictitious accounts of monster sharks such as that portrayed in Peter Benchley's book Jaws and the Steven Spielberg movie of the same name that became a worldwide hit in 1975.
Mass killing of sharks followed, leading to several species becoming endangered. Environmentalists claim the killing mood and fear of sharks is exacerbated by sensationalist reports in the media, a trend they say continues whenever an attack occurs.
But there are those who disagree vehemently and warn that the soft attitude to sharks gives people a false and dangerous sense of security.
Fritz Herscheid is one of them. Herscheid, a former salvage diver who operated a lucrative business recovering scrap metal and shipwreck treasures in Papua New Guinea waters during the 1960s and 70s, had to share his encounters with sharks, including tigers and hammerheads, and he didn't like it.
'I would like to see every dangerous shark dead,' Herscheid insists. 'If I could find a genetic way of killing all whites, tigers and bull sharks, I'd kill all of them.'
Bold words, but Herscheid, who owns a broker business in Cairns, refuses to back off.
'Humans come first and animals come second. We have as much right in the water as them and if they can't be kept away from people, then get rid of them.
'My son is a keen surfer, and if he was killed by a shark I'd be a Vic Hislop, all my life killing sharks.'
Hislop's name is known to most Australians. Think sharks, think Hislop, shark hunter.
Hislop hasn't changed his attitude towards sharks in four decades. He maintains hardcore greenies cover up the truth about shark attacks and that many people presumed missing and drowned at sea have in fact been taken by sharks.
He is mocked in scientific circles as a shark killer with no real knowledge of the creatures he hunts. To others, however, he is a valiant sea warrior ridding our coastline of man-eating predators.
Prominent underwater photographers and documentary filmmakers Ron and Valerie Taylor summed up the prevailing conservation attitude to Hislop when Ron Taylor told me in 1991 that they refused to discuss the man or his claims.
'Hislop is the only person in the world we don't want to be associated with,' he said.
'No wonder!' Hislop replied. 'They won't front me on television to debate this issue. I've challenged them, but they're not game because they know I can back up what I'm saying.'
After a spate of shark attacks around the Australian coast early last year, Hislop was adamant in his long-held belief that bureaucrats and government officials, aided and abetted by conservation groups and tourism dive operators, lead a conspiracy to cover up the true figures relating to shark attack fatalities.
'The shark protection industry doesn't like me because I tell the truth,' Hislop says.
'I won't change. I've been right all along. Shark fatalities around Australia and the world are continually manipulated to suit the shark industry.'
Hislop continues to hunt sharks from his base at Hervey Bay, Queensland, where his popular shark show continues to attract enthusiastic crowds.
'The people who are hiding the truth about great white sharks are the ones who will stay out of the water and die in bed. They have no worries, but what about their children and grandchildren?
'Some of them are sure to be taken because I predict the coming years will see a great increase in fatal attacks, all because of blatant lies and bureaucratic stupidity.'
One of the issues that intrigues me is the question of so-called rogue sharks - sometimes referred to as serial killers of the sea - those that attack and kill humans in numbers, at the same time, in the same place.
Do rogue sharks exist or are multiple attacks merely coincidental and random? That such attacks sometimes occur is a fact, but the reasons why are in dispute.
In one little-known but terrifying incident, a tiger shark attacked three people in one day in Madang Harbour in PNG, killing two.
Nine days later it struck again, claiming its third human life.
The killing spree began on February 7, 1996. On that day, the calm waters of this peaceful town were turned into a bloody slaughterhouse as the shark stalked the harbour. In little more than a week, three lives were lost in four attacks.
Tim Rowland, an expatriate Australian who has operated adventure dive tours in PNG and Solomon Islands for the past four decades, said it wasn't until the next day that the attacks became general knowledge.
'Very few people would have known on the day they happened,' Rowland told me. 'The two who went in after the first wouldn't have known.
'That shark basically had breakfast, lunch and dinner.'
A week later, Rowland was scuba diving with a student when they were confronted by a 4m tiger shark. Rowland had entered the water knowing the risk, but experience and common sense ensured he was alert to danger.
'We were supposed to do a surface swim but because I thought the shark might still be around I decided we'd go underwater,' Rowland says.
'I'm glad we did because that's when we ran into him. We were in a little alcove when the shark came in over the top and brushed against me.
'I heard the student scream through his regulator, so I grabbed him and pulled him down to the bottom. I was certain this was the shark that had killed those people.'
Rowland punched the shark as it made several passes before moving off.
'I was amazed at how slow the shark was moving. It was like slow motion, and I was thinking when is he going to open his mouth and take a chomp at us. He was a big shark.'
Rowland and the student made it to safety. A 4m tiger shark was caught 11 days after the first attacks. He has no doubt it was Madang's killer shark.
Australian surgeon V. M. Coppleson was one of the first modern scientists to develop the rogue shark theory in his attempt to understand and explain why sharks occasionally attack humans in numbers.
In his 1958 book Shark Attack, Coppleson used the term rogue many times as he documented multiple attacks across the world, including several serial fatal attack patterns on Sydney's beaches in the 20s and 30s.
He also recorded a series of five fatal shark attacks in four years on the sparsely populated beaches north of Cairns in the 40s.
In an article published in the Medical Journal of Australia, Coppleson wrote: 'A rogue shark, if the theory is correct, and evidence appears to prove it to the hilt - like the man-eating tiger - is a killer which, having experienced the deadly sport of killing or mauling a human, goes in search of similar game. The theory is supported by the pattern and frequency of many attacks.'
The most famous example of multiple shark attacks took place on the New Jersey coast of the US during the summer of 1916, when four people were killed in 12 days. Such a series of attacks was unknown at the time.
Disbelief, fear and confusion reigned until a great white shark was caught in Raritan Bay with human bones and flesh in its stomach.
In December 1957, the South African city of Durban was the focal point for what is believed to be a world record for the most shark attacks in a single place in a short time.
Beginning in what became known as Black December and continuing for 107 days, seven attacks took place at unprotected beaches south of the city, claiming five lives.
But the rogue shark concept is almost universally dismissed in contemporary scientific thought.
John West, who collates statistics for Sydney's Taronga Zoo's Australian Shark Attack File, rejects the notion of rogue sharks that specifically target humans.
He points out that Coppleson's rogue shark theory, while credible at the time, is discredited.
'Modern analysis of shark attack data does not support the theory of a rogue shark as a viable explanation for the vast majority of shark attacks, whether clustered or not,' West says.
'Some of the clusters of attacks he noted were many kilometres apart, or months or even years apart, and could not realistically relate to a single rogue shark.'
John Stevens, a senior principal research scientist at CSIRO Marine and Atmospheric Research in Hobart who has 30 years' experience studying sharks, agrees that Coppleson's rogue shark theory is just that, a theory.
'There is no scientific basis for it. It's more likely that favourable conditions for sharks at the time of an attack just brought several into the area around the same time,' Stevens says.
'There is no evidence for one individual being responsible for a chain of attacks.'
Shark attack survivor Rodney Fox, the diver who was almost bitten in half by a great white in 1963 and now owns and operates the Rodney Fox Great White Shark Expeditions at Port Lincoln in South Australia, agrees.
'There is no evidence that a rogue shark, a killer with a taste for human blood, has ever existed in the past or exists now,' he says.
But it's hard to deny the evidence of some multiple attacks being the deadly work of a single shark, and that day of horror in Madang Harbour comes to mind.
Three attacks in one day. Two people dead. One shark.
Robert Reid is the author of Shark! Killer Tales from the Dangerous Depths published by Allen & Unwin and available next Tuesday.
- Sent using Google Toolbar"
Sunday, November 21, 2010
Bull Sharks Jump Out Of Water In Brisbane River
Bull Sharks Jump Out Of Water In Brisbane River:
"Leaping sharks are no bull"
Sean Baumgart
September 6, 2010
Bull sharks' behaviour baffles scientists.
It's a phenomenon with which Brisbane River boaties are familiar, but scientists are at a loss to explain.
Every year as temperatures rise, bull sharks can be seen leaping from the water and spinning through the air, sparking wonder among spectators and researchers alike.
University of Queensland professor in zoology Craig Franklin says despite up to a thousand bull sharks living in the river winding its way through the state capital, much of their behaviour is a mystery.
Advertisement: Story continues below
Particularly confounding is the sight of the sharks getting air time during warmer months.
It is a spectacle ferry drivers say they catch sight of up to four times a week.
Craig Wilkins, who has spent years on the river as a City Cat master and at the helm of the Kookaburra Queen, says the wide stretch of river at Bulimba is a common spot for the behaviour.
“The warmer the water, the more times you will see them jumping,” he said. As the sun gets up, that's when you will see them jumping.
“About two years ago the river was a little bit cleaner than usual and everybody was seeing them. You ask any City Cat master, they'll say the same thing. They see them jumping all the time.”
As well, their aerials show the sharks are also more active underwater as the river at this time of year.
Sharks found upstream are normally less than 1.5m long and pose little threat to people.
However, dog owners have been warned to keep their pets out of the river at dusk and dawn, when sharks are most active.
There have been numerous reports of dogs being taken from the river's edge and even instances of more ambitious sharks taking on larger prey.
In 2005, Ipswich locals were shocked after a bull shark attacked a race horse being put through its paces in the Brisbane River at Kholo.
The attack came just weeks after a teenager was bitten on the head and finger at Karalee.
One ferry driver recently told of seeing a Chihuahua snapped up in shallow water at the edge of the river and Professor Franklin said small dogs would be attractive to sharks.
“Small snacks like [Chihuahuas] could be within the size range of prey items that a bull shark would take,” he said.
“You wouldn't want to let your dog go for a swim around dusk and dawn. That's when they are most likely to be feeding.”
A “cosmopolitan” creature found in tropical and sub-tropical waterways around the world, the bull shark has long baffled scientists with its behaviour in Indonesia, Thailand, Fiji and Florida.
In some cases they have been observed leaping for bats, but by and large their motive is a mystery, according to Professor Franklin.
“I've got no idea to tell you the truth,” he said. “Whether it's to scare prey out, I've got no idea why they do that.
“I've seen it and it tends to be the small ones.”
City Cat and ferry drivers say they often see it during the long hours they spend on the waterway.
They have even ventured theories on why it happens.
Mr Wilkins said the manoeuvre could be a type of housekeeping.
“My belief is, and I don't know if it is accurate, but my belief is that they are getting rid of parasites and that's why they spin around so fast,” he said.
“That's what we see as we are driving along occasionally is them jumping up and doing a bit of a spin and hitting the water again. They're usually about four foot long and the biggest I've ever seen was about six foot, I guess.”
His theory was echoed by another ferry driver who spoke to brisbanetimes.com.au, but Professor Franklin wasn't sold on the idea.
“I doubt that,” he said. “There are external parasites that they can have, but I've never heard that it's a successful strategy to remove parasites.”
Professor Franklin said it was possible bull sharks were among those filmed feeding on a school of bait fish off Teewah Beach north of Noosa on Friday and were often found in the open ocean.
But he said what set them apart from other species was their ability to survive in fresh water thanks to being able to retain salt in their bodies.
He said the sharks give birth near the mouth of the river, with the 50cm pups heading upstream, where they would live for up to four years until they venture into the ocean in search of larger prey.
“I think to be in a state capital city and to have bull sharks in our waterways is a wonderful thing. They are undoubtedly an incredible animal to have in our waterways,” he said.
Around the world, more fatalities are attributed to bull sharks than any other species.
In the past decade bull sharks have been blamed for deaths in the Gold Coast canal system, and an attack which killed a teenage girl at North Stradbroke Island in 2006.
“You could almost say they are a cosmopolitan shark in that most capital cities are built around river systems, they are circum-global, so right around the globe, so the likelihood of people being injured or killed is higher,” said Professor Franklin.
“But they don't target humans. People need to realise that. They are opportunistic feeders. All we have to do is modify our behaviour and be careful where we swim and the time at which we swim.
“You look at the unfortunate incidents on the Gold Coast in the canals where people were taken and they were swimming around at night time or dusk or dawn.”
"Leaping sharks are no bull"
Sean Baumgart
September 6, 2010
Bull sharks' behaviour baffles scientists.
It's a phenomenon with which Brisbane River boaties are familiar, but scientists are at a loss to explain.
Every year as temperatures rise, bull sharks can be seen leaping from the water and spinning through the air, sparking wonder among spectators and researchers alike.
University of Queensland professor in zoology Craig Franklin says despite up to a thousand bull sharks living in the river winding its way through the state capital, much of their behaviour is a mystery.
Advertisement: Story continues below
Particularly confounding is the sight of the sharks getting air time during warmer months.
It is a spectacle ferry drivers say they catch sight of up to four times a week.
Craig Wilkins, who has spent years on the river as a City Cat master and at the helm of the Kookaburra Queen, says the wide stretch of river at Bulimba is a common spot for the behaviour.
“The warmer the water, the more times you will see them jumping,” he said. As the sun gets up, that's when you will see them jumping.
“About two years ago the river was a little bit cleaner than usual and everybody was seeing them. You ask any City Cat master, they'll say the same thing. They see them jumping all the time.”
As well, their aerials show the sharks are also more active underwater as the river at this time of year.
Sharks found upstream are normally less than 1.5m long and pose little threat to people.
However, dog owners have been warned to keep their pets out of the river at dusk and dawn, when sharks are most active.
There have been numerous reports of dogs being taken from the river's edge and even instances of more ambitious sharks taking on larger prey.
In 2005, Ipswich locals were shocked after a bull shark attacked a race horse being put through its paces in the Brisbane River at Kholo.
The attack came just weeks after a teenager was bitten on the head and finger at Karalee.
One ferry driver recently told of seeing a Chihuahua snapped up in shallow water at the edge of the river and Professor Franklin said small dogs would be attractive to sharks.
“Small snacks like [Chihuahuas] could be within the size range of prey items that a bull shark would take,” he said.
“You wouldn't want to let your dog go for a swim around dusk and dawn. That's when they are most likely to be feeding.”
A “cosmopolitan” creature found in tropical and sub-tropical waterways around the world, the bull shark has long baffled scientists with its behaviour in Indonesia, Thailand, Fiji and Florida.
In some cases they have been observed leaping for bats, but by and large their motive is a mystery, according to Professor Franklin.
“I've got no idea to tell you the truth,” he said. “Whether it's to scare prey out, I've got no idea why they do that.
“I've seen it and it tends to be the small ones.”
City Cat and ferry drivers say they often see it during the long hours they spend on the waterway.
They have even ventured theories on why it happens.
Mr Wilkins said the manoeuvre could be a type of housekeeping.
“My belief is, and I don't know if it is accurate, but my belief is that they are getting rid of parasites and that's why they spin around so fast,” he said.
“That's what we see as we are driving along occasionally is them jumping up and doing a bit of a spin and hitting the water again. They're usually about four foot long and the biggest I've ever seen was about six foot, I guess.”
His theory was echoed by another ferry driver who spoke to brisbanetimes.com.au, but Professor Franklin wasn't sold on the idea.
“I doubt that,” he said. “There are external parasites that they can have, but I've never heard that it's a successful strategy to remove parasites.”
Professor Franklin said it was possible bull sharks were among those filmed feeding on a school of bait fish off Teewah Beach north of Noosa on Friday and were often found in the open ocean.
But he said what set them apart from other species was their ability to survive in fresh water thanks to being able to retain salt in their bodies.
He said the sharks give birth near the mouth of the river, with the 50cm pups heading upstream, where they would live for up to four years until they venture into the ocean in search of larger prey.
“I think to be in a state capital city and to have bull sharks in our waterways is a wonderful thing. They are undoubtedly an incredible animal to have in our waterways,” he said.
Around the world, more fatalities are attributed to bull sharks than any other species.
In the past decade bull sharks have been blamed for deaths in the Gold Coast canal system, and an attack which killed a teenage girl at North Stradbroke Island in 2006.
“You could almost say they are a cosmopolitan shark in that most capital cities are built around river systems, they are circum-global, so right around the globe, so the likelihood of people being injured or killed is higher,” said Professor Franklin.
“But they don't target humans. People need to realise that. They are opportunistic feeders. All we have to do is modify our behaviour and be careful where we swim and the time at which we swim.
“You look at the unfortunate incidents on the Gold Coast in the canals where people were taken and they were swimming around at night time or dusk or dawn.”
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